Inks for 3d printing

ABSTRACT

In one aspect, inks for use with a three-dimensional printing system are described herein. In some embodiments, an ink described herein is a composite ink. Such a composite ink, in some cases, comprises an optically transparent or substantially transparent carrier ink comprising a curable material; and a colorant dispersed in the carrier ink in an amount of about 0.01 to 5 weight %, based on the total weight of the composite ink.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/040,676, filed on Jul. 20, 2018, which is a continuation of U.S.patent application Ser. No. 14/644,701, filed on Mar. 11, 2015, now U.S.Pat. No. 10,052,861, issued on Aug. 21, 2018, which claims prioritypursuant to 35 U.S.C. § 119 to U.S. Provisional Patent Application Ser.No. 61/950,906, filed on Mar. 11, 2014, and to U.S. Provisional PatentApplication Ser. No. 61/978,795, filed on Apr. 11, 2014, each of whichis hereby incorporated by reference in its entirety.

FIELD

The present invention relates to inks and, in particular, to pigmentedinks for use with three-dimensional (3D) printing systems.

BACKGROUND

Commercially available 3D printers, such as the ProJet™ 3D Printersmanufactured by 3D Systems of Rock Hill, S.C., use inks, which are alsoknown as build materials, that are jetted through a print head as aliquid to form various 3D objects or parts. Other 3D printing systemsalso use an ink that is jetted through a print head. In some instances,the ink is solid at ambient temperatures and converts to liquid atelevated jetting temperatures. In other instances, the ink is liquid atambient temperatures.

Some inks can include one or more colorants or pigments to providecolored printed parts. However, many such inks are much more highlypigmented than necessary or desired to provide colored printed parts.Moreover, the presence of pigments in many inks can interfere with thejettability, stability, and/or curability of the inks. In addition, thepigment load of some pigmented inks can require different types and/oramounts of photoinitiators to obtain appropriate curing of inks havingdifferent colors, which can result in decreased efficiency and/orincreased cost of a 3D printing process.

Therefore, there exists a need for improved inks for 3D printing,including for colored 3D printing applications.

SUMMARY

In one aspect, inks for use with a 3D printer are described hereinwhich, in some embodiments, may offer one or more advantages over priorinks. In some embodiments, for example, an ink described herein providesprinted parts that have improved chroma or chromaticity. In addition, insome cases, an ink described herein is a curable ink having excellentjettability and/or high colloidal stability.

In some embodiments, an ink for use in a 3D printing system describedherein is a composite ink. A composite ink, in some instances, comprisesan optically transparent or substantially transparent carrier inkcomprising a curable material; and a colorant dispersed in the carrierink in an amount of about 0.01 to 5 weight %, based on the total weightof the composite ink. Further, in some cases, a chroma of the compositeink at a given thickness of the composite ink is within about 20% of amaximum chroma of the colorant in the composite ink. Moreover, thecolorant of a composite ink described herein can be a particulatepigment or a molecular dye. Further, in some embodiments, the carrierink of a composite ink described herein has an optical transparency ofat least about 70% transmission, at least about 80% transmission, or atleast about 90% transmission between 350 nm and 750 nm, all at a giventhickness, such as a thickness between about 0.01 and 10 mm, betweenabout 1 and 10 mm, between about 0.2 and 1 mm, between about 0.3 and 0.8mm, between about 1 and 5 mm, or between about 5 and 10 mm.Additionally, in some instances, a composite ink described hereinfurther comprises one or more additives selected from the groupconsisting of photoinitiators, inhibitors, stabilizing agents,sensitizers, and combinations thereof.

In another aspect, methods of printing a 3D article are describedherein. In some embodiments, a method of printing a 3D article comprisesselectively depositing layers of a composite ink described herein in afluid state onto a substrate. For example, in some cases, the compositeink comprises an optically transparent or substantially transparentcarrier ink comprising a curable material; and a colorant dispersed inthe carrier ink in an amount of about 0.01 to 5 weight %, based on thetotal weight of the composite ink. Further, the layers of a compositeink can be deposited according to an image of the 3D article in acomputer readable format. Moreover, in some cases, one or more layers ofa composite ink described herein has a thickness of about 0.03 to about5 mm.

In addition, in some embodiments, a method described herein furthercomprises supporting at least one of the layers of the composite inkwith a support material. A method described herein can also comprisecuring the layers of the composite ink.

In another aspect, printed 3D articles are described herein. In someembodiments, a printed 3D article is formed from a composite inkdescribed herein, such as a composite ink comprising an opticallytransparent or substantially transparent carrier ink comprising acurable material; and a colorant dispersed in the carrier ink in anamount of about 0.01 to 5 weight %, based on the total weight of thecomposite ink.

In other embodiments, a printed 3D article comprises a core componentcomprising a plurality of layers formed from an opaque ink; and a shellcomponent comprising a plurality of layers disposed over a surface ofthe core component. At least one layer of the shell component is formedfrom a composite ink described herein, such as a composite inkcomprising an optically transparent or substantially transparent carrierink comprising a curable material; and a colorant dispersed in thecarrier ink in an amount of about 0.01 to 5 weight %, based on the totalweight of the composite ink. Moreover, in some instances, at least onelayer of the shell component formed from a composite ink has a thicknessof about 0.03 to about 5 mm.

Further, in some cases, an article described herein can comprise a shellcomponent formed from a plurality of differing inks in a layer-by-layermanner, where the plurality of differing inks can include a plurality ofdiffering composite inks described herein. For example, in someembodiments, the shell component of an article described hereincomprises one or more layers formed from a first composite inkcomprising a first optically transparent or substantially transparentcarrier ink comprising a curable material, and a first colorantdispersed in the first carrier ink in an amount of about 0.01 to 5weight %, based on the total weight of the first composite ink; and oneor more layers formed from a second composite ink comprising a secondoptically transparent or substantially transparent carrier inkcomprising a curable material, and a second colorant dispersed in thesecond carrier ink in an amount of about 0.01 to 5 weight %, based onthe total weight of the second composite ink. In such cases, the firstcomposite ink and the second composite ink can be different inks. Forexample, in some embodiments, the chemical identity and/or amount of thefirst colorant of the first composite ink can differ from the chemicalidentity and/or amount of the second colorant of the second compositeink.

These and other embodiments are described in greater detail in thedetailed description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates plots of chroma versus layer thickness for variouspigments dispersed in a carrier ink.

FIG. 2 illustrates plots of optical density versus layer thickness forvarious pigments dispersed in a carrier ink.

FIG. 3 illustrates plots of lightness versus layer thickness for variouspigments dispersed in a carrier ink.

FIG. 4 illustrates schematically a sectional view of an articleaccording to one embodiment described herein.

DETAILED DESCRIPTION

Embodiments described herein can be understood more readily by referenceto the following detailed description, examples, and drawings. Elements,apparatus and methods described herein, however, are not limited to thespecific embodiments presented in the detailed description, examples,and drawings. It should be recognized that these embodiments are merelyillustrative of the principles of the present invention. Numerousmodifications and adaptations will be readily apparent to those of skillin the art without departing from the spirit and scope of the invention.

In addition, all ranges disclosed herein are to be understood toencompass any and all subranges subsumed therein. For example, a statedrange of “1.0 to 10.0” should be considered to include any and allsubranges beginning with a minimum value of 1.0 or more and ending witha maximum value of 10.0 or less, e.g., 1.0 to 5.3, or 4.7 to 10.0, or3.6 to 7.9.

All ranges disclosed herein are also to be considered to include the endpoints of the range, unless expressly stated otherwise. For example, arange of “between 5 and 10” should generally be considered to includethe end points 5 and 10.

Further, when the phrase “up to” is used in connection with an amount orquantity, it is to be understood that the amount is at least adetectable amount or quantity. For example, a material present in anamount “up to” a specified amount can be present from a detectableamount and up to and including the specified amount.

The terms “three-dimensional printing system,” “three-dimensionalprinter,” “printing,” and the like generally describe various solidfreeform fabrication techniques for making three-dimensional articles orobjects by selective deposition, jetting, fused deposition modeling,multijet modeling, and other additive manufacturing techniques now knownin the art or that may be known in the future that use a build materialor ink to fabricate three-dimensional objects.

I. Composite Inks

In one aspect, composite inks for use with a 3D printer are describedherein. In some embodiments, a composite ink described herein comprisesan optically transparent or substantially transparent carrier inkcomprising a curable material; and a colorant dispersed in the carrierink in an amount of about 0.01 to 5 weight %, based on the total weightof the composite ink. In some cases, the colorant is present in thecarrier ink in an amount between about 0.01 and 3 weight %, betweenabout 0.01 and 1 weight %, between about 0.05 and 5 weight %, betweenabout 0.05 and 3 weight %, between about 0.05 and 1 weight %, betweenabout 0.1 and 5 weight %, between about 0.1 and 3 weight %, or betweenabout 0.1 and 1 weight %.

Further, in some cases, a chroma of the composite ink at a giventhickness of the composite ink is within about 20%, within about 15%,within about 10%, or within about 5% of a maximum chroma of the colorantin the composite ink. The “chroma” of a composite ink or colorant, forreference purposes herein, refers to the radial component of the polarcoordinates of the color of the composite ink or colorant inchromaticity space, such as the CIE 1931 chromaticity space. Further, insome embodiments, a maximum chroma of a composite ink or colorant can bea function of the thickness of the composite ink, including thethickness of a layer formed by the composite ink in a manner describedherein. Thus, in some embodiments, the colorant loading of a compositeink described herein can be selected to maximize the chroma of thecomposite ink, including for a specific desired layer thickness of thecomposite ink.

Moreover, the colorant of a composite ink described herein can be aparticulate colorant, such as a particulate pigment, or a molecularcolorant, such as a molecular dye. Any such particulate or molecularcolorant not inconsistent with the objectives of the present disclosuremay be used. In some cases, for instance, the colorant of a compositeink comprises an inorganic pigment, such as TiO₂ and ZnO. In someembodiments, the colorant of a composite ink comprises a colorant foruse in a RGB, sRGB, CMY, CMYK, L*a*b*, or Pantone® colorization scheme.Moreover, in some cases, a particulate colorant described herein has anaverage particle size of less than 500 nm, such as an average particlesize of less than 400 nm, less than 300 nm, less than 250 nm, less than200 nm, or less than 150 nm. In some instances, a particulate coloranthas an average particle size of 50-1000 nm, 50-500 nm, 50-400 nm, 50-300nm, 50-200 nm, 70-500 nm, 70-300 nm, 70-250 nm, or 70-200 nm.

Further, in some embodiments, the carrier ink of a composite inkdescribed herein can have a high optical transparency, including in thevisible region of the electromagnetic spectrum. In some cases, forinstance, the carrier ink has an optical transparency of at least about70% transmission, at least about 80% transmission, at least about 90%transmission, or at least about 95% transmission between about 350 nmand about 750 nm, at a given thickness, such as a thickness of about0.01 to 10 mm, about 0.2 to 1 mm, about 0.3 to 0.8 mm, about 1 to 10 mm,about 1 to 5 mm, or about 5 to 10 mm. In some cases, a carrier ink has atransparency of at least about 98% or at least about 99% transmissionbetween about 350 nm and about 750 nm, at a given thickness, such as athickness of about 0.01 to 10 mm, about 0.2 to 1 mm, about 0.3 to 0.8mm, about 1 to 10 mm, about 1 to 5 mm, or about 5 to 10 mm. Moreover, insome instances, a carrier ink described herein has an opticaltransparency between about 70% and about 95%, between about 80% andabout 99.99%, or between about 90% and about 95% transmission atwavelengths between about 350 nm and about 750 nm, at a given thickness,such as a thickness of 0.1 to 10 mm, about 0.2 to 1 mm, about 0.3 to 0.8mm, about 1 to 10 mm, about 1 to 5 mm, or about 5 to 10 mm. Carrier inkshaving an optical transparency described herein can facilitate use ofthe composite inks in 3D printing colorization processes wherein theperceived color of a 3D printed article is based on the dithering orhalftoning of discrete colors in the z-direction of the part, which isorthogonal or substantially orthogonal to the surface of the part,rather than in the x- and y-directions along the surface of the part.

In addition, carrier inks described herein comprise a curable material.The curable material can be present in the carrier ink in any amount notinconsistent with the objectives of the present disclosure. In somecases, the curable material is present in an amount up to about 99weight %, up to about 95 weight %, up to about 90 weight %, or up toabout 80 weight %, based on the total weight of the carrier ink. In somecases, a composite ink described herein comprises about 10-95 weight %curable material, based on the total weight of the carrier ink. In someembodiments, a carrier ink comprises about 20-80 weight % curablematerial, about 30-70 weight % curable material, or about 70-90 weight %curable material.

Moreover, any curable material not inconsistent with the objectives ofthe present disclosure may be used. In some cases, a curable materialcomprises one or more polymerizable components. A “polymerizablecomponent,” for reference purposes herein, comprises a component thatcan be polymerized or cured to provide a 3D printed article or object.Polymerizing or curing can be carried out in any manner not inconsistentwith the objectives of the present disclosure. In some embodiments, forinstance, polymerizing or curing comprises irradiating withelectromagnetic radiation having sufficient energy to initiate apolymerization or cross-linking reaction. For instance, in someembodiments, ultraviolet (UV) radiation can be used.

Further, any polymerizable component not inconsistent with theobjectives of the present disclosure may be used. In some embodiments, apolymerizable component comprises a monomeric chemical species, such asa chemical species having one or more functional groups or moieties thatcan react with the same or different functional groups or moieties ofanother monomeric chemical species to form one or more covalent bonds,such as in a polymerization reaction. A polymerization reaction, in someembodiments, comprises a free radical polymerization, such as thatbetween points of unsaturation, including points of ethylenicunsaturation. In some embodiments, a polymerizable component comprisesat least one ethyleneically unsaturated moiety, such as a vinyl group orallyl group. In some embodiments, a polymerizable component comprises anoligomeric chemical species capable of undergoing additionalpolymerization, such as through one or more points of unsaturation asdescribed herein. In some embodiments, a polymerizable componentcomprises one or more monomeric chemical species and one or moreoligomeric chemical species described herein. A monomeric chemicalspecies and/or an oligomeric chemical species described herein can haveone polymerizable moiety or a plurality of polymerizable moieties.

In some embodiments, a polymerizable component comprises one or morephoto-polymerizable or photo-curable chemical species. Aphoto-polymerizable chemical species, in some embodiments, comprises aUV-polymerizable chemical species. In some embodiments, a polymerizablecomponent is photo-polymerizable or photo-curable at wavelengths rangingfrom about 300 nm to about 400 nm. Alternatively, in some embodiments, apolymerizable component is photo-polymerizable at visible wavelengths ofthe electromagnetic spectrum.

In some embodiments, a polymerizable component described hereincomprises one or more species of (meth)acrylates. As used herein, theterm “(meth)acrylate” includes acrylate or methacrylate or mixtures orcombinations thereof. In some embodiments, a polymerizable componentcomprises an aliphatic polyester urethane acrylate oligomer, a urethane(meth)acrylate resin, and/or an acrylate amine oligomeric resin, such asEBECRYL 7100. In some embodiments, a UV polymerizable or curable resinor oligomer can comprise any methacrylate or acrylate resin whichpolymerizes in the presence of a free radical photoinitiator, isthermally stable in an exposed state for at least one week at a jettingtemperature and for at least 4 weeks in an enclosed state, and/or has aboiling point greater than the jetting temperature. In some embodiments,a polymerizable component has a flash point above the jettingtemperature.

Urethane (meth)acrylates suitable for use in inks described herein, insome embodiments, can be prepared in a known manner, typically byreacting a hydroxyl-terminated urethane with acrylic acid or methacrylicacid to give the corresponding urethane (meth)acrylate, or by reactingan isocyanate-terminated prepolymer with hydroxyalkyl acrylates ormethacrylates to give the urethane (meth)acrylate. Suitable processesare disclosed, inter alia, in EP-A 114 982 and EP-A 133 908. The weightaverage molecular weight of such (meth)acrylate oligomers is generallyin the range from about 400 to 10,000, or from about 500 to 7,000.Urethane (meth)acrylates are also commercially available from theSARTOMER Company under the product names CN980, CN981, CN975 and CN2901,or from Bomar Specialties Co. (Winsted, Conn.) under the product nameBR-741. In some embodiments described herein, a urethane (meth)acrylateoligomer has a viscosity ranging from about 140,000 cP to about 160,000cP at about 50° C. or from about 125,000 cP to about 175,000 cP at about50° C. when measured in a manner consistent with ASTM D2983. In someembodiments described herein, a urethane (meth)acrylate oligomer has aviscosity ranging from about 100,000 cP to about 200,000 cP at about 50°C. or from about 10,000 cP to about 300,000 cP at about 50° C. whenmeasured in a manner consistent with ASTM D2983.

In some embodiments, a polymerizable component comprises one or more lowmolecular weight materials, such as methacrylates, dimethacrylates,triacrylates, and diacrylates, which can be used in a variety ofcombinations. In some embodiments, for example, a polymerizablecomponent comprises one or more of tetrahydrofurfuryl methacrylate,triethylene glycol dimethacrylate, 2-phenoxyethyl methacrylate, laurylmethacrylate, ethoxylated trimethylolpropane triacrylate, tricyclodecanedimethanol diacrylate, 2-phenoxyethylacrylate, triethylene glycoldiacrylate, a monofunctional aliphatic urethane acrylate, polypropyleneglycol monomethacrylate, polyethylene glycol monomethacrylate,cyclohexane dimethanol diacrylate, and tridecyl methacrylate.

In some embodiments, a polymerizable component comprises diacrylateand/or dimethacrylate esters of aliphatic, cycloaliphatic or aromaticdiols, including 1,3- or 1,4-butanediol, neopentyl glycol,1,6-hexanediol, diethylene glycol, triethylene glycol, tetraethyleneglycol, polyethylene glycol, tripropylene glycol, ethoxylated orpropoxylated neopentyl glycol, 1,4-dihydroxymethylcyclohexane,2,2-bis(4-hydroxycyclohexyl)propane or bis(4-hydroxycyclohexyl)methane,hydroquinone, 4,4′-dihydroxybiphenyl, bisphenol A, bisphenol F,bisphenol S, ethoxylated or propoxylated bisphenol A, ethoxylated orpropoxylated bisphenol F or ethoxylated or propoxylated bisphenol S.

A polymerizable component, in some embodiments, comprises one or moretri(meth)acrylates. In some embodiments, tri(meth)acrylates comprise1,1-trimethylolpropane triacrylate or methacrylate, ethoxylated orpropoxylated 1,1,1-trimethylolpropanetriacrylate or methacrylate,ethoxylated or propoxylated glycerol triacrylate, pentaerythritolmonohydroxy triacrylate or methacrylate, or tris(2-hydroxy ethyl)isocyanurate triacrylate.

In some embodiments, a polymerizable component of an ink describedherein comprises one or more higher functional acrylates ormethacrylates such as dipentaerythritol monohydroxy pentaacrylate orbis(trimethylolpropane) tetraacrylate. In some embodiments, a(meth)acrylate of an ink has a molecular weight ranging from about 250to 700.

In some embodiments, a polymerizable component comprises allyl acrylate,allyl methacrylate, methyl (meth)acrylate, ethyl (meth)acrylate,n-propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl(meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate,n-octyl (meth)acrylate, n-decyl (meth)acrylate and n-dodecyl(meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2- and 3-hydroxypropyl(meth)acrylate, 2-methoxyethyl(meth)acrylate, 2-ethoxyethyl(meth)acrylate and 2- or 3-ethoxypropyl (meth)acrylate,tetrahydrofurfuryl methacrylate, 2-(2-ethoxyethoxy)ethyl acrylate,cyclohexyl methacrylate, 2-phenoxyethyl acrylate, glycidyl acrylate,isodecyl acrylate, or a combination thereof.

Additional non-limiting examples of species of polymerizable componentsuseful in some embodiments described herein include the following:isobornyl acrylate (IBOA), commercially available from SARTOMER underthe trade name SR 506A; isobornyl methacrylate, commercially availablefrom SARTOMER under the trade name SR 423A; alkoxylatedtetrahydrofurfuryl acrylate, commercially available from SARTOMER underthe trade name SR 611; monofunctional urethane acrylate, commerciallyavailable from RAHN USA under the trade name GENOMER 1122; aliphaticurethane diacrylate, commercially available from ALLNEX under the tradename EBECRYL 8402; triethylene glycol diacrylate, commercially availablefrom SARTOMER under the trade name SR 272; triethylene glycoldimethacrylate, commercially available from SARTOMER under the tradename SR 205; tricyclodecane dimethanol diacrylate, commerciallyavailable from SARTOMER under the trade name SR 833S; tris(2-hydroxyethyl)isocyanurate triacrylate, commercially available from SARTOMERunder the trade name SR 368; and 2-phenoxyethyl acrylate, commerciallyavailable from SARTOMER under the trade name SR 339. Other commerciallyavailable curable materials may also be used.

Carrier inks described herein, in some embodiments, further comprise oneor more additives. In some embodiments, a carrier ink described hereinfurther comprises one or more additives selected from the groupconsisting of photoinitiators, inhibitors, stabilizing agents,sensitizers, and combinations thereof. For example, in some embodiments,an ink further comprises one or more photoinitiators. Any photoinitiatornot inconsistent with the objectives of the present disclosure can beused. In some embodiments, a photoinitiator comprises an alpha-cleavagetype (unimolecular decomposition process) photoinitiator or a hydrogenabstraction photosensitizer-tertiary amine synergist, operable to absorblight preferably between about 250 nm and about 400 nm or between about300 nm and about 385 nm, to yield free radical(s).

Examples of alpha cleavage photoinitiators are Irgacure 184 (CAS947-19-3), Irgacure 369 (CAS 119313-12-1), and Irgacure 819 (CAS162881-26-7). An example of a photosensitizer-amine combination isDarocur BP (CAS 119-61-9) with diethylaminoethylmethacrylate.

In some embodiments, suitable photoinitiators comprise benzoins,including benzoin, benzoin ethers, such as benzoin methyl ether, benzoinethyl ether and benzoin isopropyl ether, benzoin phenyl ether andbenzoin acetate, acetophenones, including acetophenone,2,2-dimethoxyacetophenone and 1,1-dichloroacetophenone, benzil, benzilketals, such as benzil dimethyl ketal and benzil diethyl ketal,anthraquinones, including 2-methylanthraquinone, 2-ethylanthraquinone,2-tert-butylanthraquinone, 1-chloroanthraquinone and2-amylanthraquinone, triphenylphosphine, benzoylphosphine oxides, forexample 2,4,6-trimethylbenzoyldiphenylphosphine oxide (Lucirin TPO),benzophenones, such as benzophenone and4,4′-bis(N,N′-dimethylamino)benzophenone, thioxanthones and xanthones,acridine derivatives, phenazine derivatives, quinoxaline derivatives or1-phenyl-1,2-propanedione, 2-O-benzoyl oxime, 1-aminophenyl ketones or1-hydroxyphenyl ketones, such as 1-hydroxycyclohexyl phenyl ketone,phenyl 1-hydroxyisopropyl ketone and 4-isopropylphenyl1-hydroxyisopropyl ketone.

In some cases, suitable photoinitiators comprise those operable for usewith a HeCd laser radiation source, including acetophenones,2,2-dialkoxybenzophenones and 1-hydroxyphenyl ketones, such as1-hydroxycyclohexyl phenyl ketone or 2-hydroxyisopropyl phenyl ketone(=2-hydroxy-2,2-dimethylacetophenone). Additionally, in some instances,suitable photoinitiators comprise those operable for use with an Arlaser radiation source including benzil ketals, such as benzil dimethylketal. In some embodiments, a photoinitiator comprises anα-hydroxyphenyl ketone, benzil dimethyl ketal or2,4,6-trimethylbenzoyldiphenylphosphine oxide or a mixture thereof.

Another class of suitable photoinitiators, in some cases, comprisesionic dye-counter ion compounds capable of absorbing actinic radiationand generating free radicals for polymerization initiation. In someembodiments, inks containing ionic dye-counter ion compounds can becured more variably with visible light within the adjustable wavelengthrange of about 400 nm to about 700 nm. Some ionic dye-counter ioncompounds and their mode of operation are disclosed in EP-A-0 223 587and U.S. Pat. Nos. 4,751,102; 4,772,530; and 4,772,541.

A photoinitiator can be present in an ink described herein in any amountnot inconsistent with the objectives of the present disclosure. In someembodiments, a photoinitiator is present in an ink in an amount of up toabout 5 weight percent, based on the total weight of the ink. In someembodiments, a photoinitiator is present in an amount ranging from about0.1 weight percent to about 5 weight percent.

In some embodiments, an ink further comprises one or more sensitizers. Asensitizer can be added to an ink to increase the effectiveness of oneor more photoinitiators that may also be present. Any sensitizer notinconsistent with the objectives of the present disclosure may be used.In some embodiments, a sensitizer comprises isopropylthioxanthone (ITX).In some embodiments, a sensitizer comprises 2-chlorothioxanthone (CTX).

A sensitizer can be present in an ink in any amount not inconsistentwith the objectives of the present disclosure. In some embodiments, asensitizer is present in an amount ranging from about 0.1 weight percentto about 2 weight percent, based on the total weight of the ink. Asensitizer, in some embodiments, is present in an amount ranging fromabout 0.5 weight percent to about 1 weight percent.

In addition, an ink described herein, in some embodiments, furthercomprises one or more polymerization inhibitors or stabilizing agents. Apolymerization inhibitor can be added to an ink to provide additionalthermal stability to the composition. Any polymerization inhibitor notinconsistent with the objectives of the present disclosure may be used.In some cases, a polymerization inhibitor comprises methoxyhydroquinone(MEHQ). A stabilizing agent, in some embodiments, comprises one or moreanti-oxidants. A stabilizing agent can comprise any anti-oxidant notinconsistent with the objectives of the present disclosure. In somecases, suitable anti-oxidants include various aryl compounds, includingbutylated hydroxytoluene (BHT), which can also be used as apolymerization inhibitor in some embodiments described herein.

A polymerization inhibitor and/or a stabilizing agent can be present inan ink in any amount not inconsistent with the objectives of the presentdisclosure. In some embodiments, a polymerization inhibitor is presentin an amount ranging from about 0.1 wt. % to about 2 wt. % or from about0.5 wt. % to about 1 wt. %. Similarly, in some cases, a stabilizingagent is present in an ink in an amount ranging from about 0.1 wt. % toabout 5 wt. %, from about 0.5 wt. % to about 4 wt. %, or from about 1wt. % to about 3 wt. %, based on the total weight of the ink.

Composite inks described herein can also exhibit a variety of otherdesirable properties. For example, a composite ink described herein canhave any freezing point, melting point, and/or other phase transitiontemperature not inconsistent with the objectives of the presentdisclosure. In some embodiments, an ink has freezing and melting pointsconsistent with temperatures used in some 3D printing systems, including3D printing systems designed for use with phase changing inks. In someembodiments, the freezing point of an ink is greater than about 40° C.In some embodiments, for example, an ink has a freezing point centeredat a temperature ranging from about 45° C. to about 55° C. or from about50° C. to about 80° C. In some embodiments, an ink has a freezing pointbelow about 40° C. or below about 30° C.

Further, in some embodiments described herein, a composite ink exhibitsa sharp freezing point or other phase transition. In some cases, forinstance, an ink freezes over a narrow range of temperatures, such as arange of about 1-10° C., about 1-8° C., or about 1-5° C. In someembodiments, an ink having a sharp freezing point freezes over atemperature range of X±2.5° C., where X is the temperature at which thefreezing point is centered (e.g., X=65° C.).

In addition, a composite ink described herein, in some cases, is fluidat jetting temperatures encountered in 3D printing systems. Moreover, insome embodiments, an ink solidifies once deposited on a surface duringthe fabrication of a three-dimensionally printed article or object.Alternatively, in other embodiments, an ink remains substantially fluidupon deposition on a surface. Solidification of an ink, in someembodiments, occurs through a phase change of the ink, such as freezing.The phase change can comprise a liquid to solid phase change or a liquidto semi-solid phase change. Further, in some instances, solidificationof an ink comprises an increase in viscosity, such as an increase inviscosity from a low viscosity state to a high viscosity state.

In some embodiments, a composite ink described herein has a viscosityprofile consistent with the requirements and parameters of one or more3D printing systems. In some embodiments, for instance, an ink describedherein has a viscosity ranging from about 8.0 cP to about 14.0 cP at atemperature of about 80° C. when measured according to ASTM standardD2983 (e.g., using a Brookfield Model DV-II+ Viscometer). In someembodiments, an ink has a viscosity ranging from about 9.5 cP to about12.5 cP at a temperature of about 80° C. An ink, in some embodiments,has a viscosity ranging from about 10.5 cP to about 12.5 cP at atemperature of about 80° C. In some embodiments, an ink has a viscosityranging from about 8.0 cP to about 10.0 cP at a temperature of about85-87° C.

In some embodiments, a composite ink described herein has a viscosityranging from about 8.0 cP to about 19.0 cP at a temperature of about 65°C. measured according to ASTM standard D2983. In some embodiments, anink described herein has a viscosity ranging from about 8.0 cP to about13.5 cP at a temperature of about 65° C. An ink, in some embodiments,has a viscosity ranging from about 11.0 cP to about 14.0 cP at atemperature of about 65° C. In some embodiments, an ink has a viscosityranging from about 11.5 cP to about 13.5 cP or from about 12.0 cP toabout 13.0 cP at a temperature of about 65° C.

Further, composite inks described herein, in some embodiments, exhibit acombination of one or more desirable features. In some embodiments, forinstance, a composite ink in the non-cured state has one or more of thefollowing properties:

1. Freezing point between about 30° C. and about 65° C.;

2. jetting viscosity of about 8 cP to about 16 cP at 70-95° C.; and

3. Thermal stability for at least 3 days at the jetting temperature.Viscosity can be measured according to ASTM D2983 (e.g., using aBrookfield Model DV-II+ Viscometer). In addition, for reference purposesherein, a “thermally stable” material exhibits no greater than about a35 percent change in viscosity over a specified time period (e.g., 3days) when measured at the specified temperature (e.g., a jettingtemperature of 85° C.) at the beginning and at the end of the timeperiod. In some embodiments, the viscosity change is no greater thanabout 30 percent or no greater than about 20 percent. In someembodiments, the viscosity change is between about 10 percent and about20 percent or between about 25 percent and about 30 percent. Moreover,in some embodiments, the change in viscosity is an increase inviscosity.

Composite inks described herein can also exhibit a variety of desirableproperties, in addition to those described hereinabove, in a curedstate. A composite ink in a “cured” state, as used herein, comprises anink that includes a curable material or polymerizable component that hasbeen at least partially polymerized and/or cross-linked. For instance,in some embodiments, a cured ink is at least about 10% polymerized orcross-linked or at least about 30% polymerized or cross-linked. In someembodiments, a cured ink is at least about 50%, at least about 70%, atleast about 80%, or at least about 90% polymerized or cross-linked. Insome embodiments, a cured ink is between about 10% and about 99%polymerized or cross-linked.

Composite inks described herein, in some embodiments, can be produced inany manner not inconsistent with the objectives of the presentdisclosure. In some embodiments, for instance, a method for thepreparation of an ink described herein comprises the steps of mixing thecomponents of the ink, melting the mixture, and filtering the moltenmixture. Melting the mixture, in some embodiments, is carried out at atemperature of about 75° C. or in a range from about 75° C. to about 85°C. In some embodiments, an ink described herein is produced by placingall components of the ink in a reaction vessel and heating the resultingmixture to a temperature ranging from about 75° C. to about 85° C. withstirring. The heating and stirring are continued until the mixtureattains a substantially homogenized molten state. In general, the moltenmixture can be filtered while in a flowable state to remove any largeundesirable particles that may interfere with jetting. The filteredmixture is then cooled to ambient temperatures until it is heated in theink jet printer.

II. Methods of Printing a 3D Article

In another aspect, methods of printing a 3D article or object aredescribed herein. In some embodiments, a method of printing a 3D articlecomprises selectively depositing layers of a composite ink describedherein in a fluid state onto a substrate. Any composite ink describedhereinabove in Section I may be used. For example, in some cases, thecomposite ink comprises an optically transparent or substantiallytransparent carrier ink comprising a curable material; and a colorantdispersed in the carrier ink in an amount of about 0.01 to 5 weight %,based on the total weight of the composite ink. Further, the layers of acomposite ink can be deposited according to an image of the 3D articlein a computer readable format. In some embodiments, the ink is depositedaccording to preselected computer aided design (CAD) parameters.

Moreover, in some cases, one or more layers of a composite ink describedherein have a thickness of about 0.03 to about 5 mm, a thickness ofabout 0.03 to about 3 mm, a thickness of about 0.03 to about 1 mm, athickness of about 0.03 to about 0.5 mm, a thickness of about 0.03 toabout 0.3 mm, a thickness of about 0.03 to about 0.2 mm, a thickness ofabout 0.05 to about 5 mm, a thickness of about 0.05 to about 1 mm, athickness of about 0.05 to about 0.5 mm, a thickness of about 0.05 toabout 0.3 mm, or a thickness of about 0.05 to about 0.2 mm. Otherthicknesses are also possible.

Further, in some cases, the substrate of a method described hereincomprises an opaque core component of the 3D article, including a corecomponent formed from an opaque ink. Thus, in some embodiments, a methodof printing a 3D article described herein comprises forming a corecomponent from an opaque ink and forming a shell component on thesurface of the core component, the shell comprising successive orsequentially stacked layers of a composite ink described herein.However, it is to be understood that the layers of the shell componentmay be stacked in a z-direction of the article, where the z-direction isnormal or substantially normal to an exterior surface of the article.Moreover, the z-direction is not necessarily the direction of 3Dprinting, where the “direction” of 3D printing refers to the directionin which sequentially deposited layers of build material are built up toform the 3D article. Instead, the direction of 3D printing may beanother direction, as needed or desired for printing a 3D article havinga desired geometry and surface colorization. In general, an articledescribed herein can be formed by defining a shell component and a corecomponent of the article as part of a rendering step, prior to slicingof the article for 3D printing. Thus, in some instances, the thinnestdimension of the slices and/or sequentially deposited layers of thearticle may be oriented perpendicular to the z-direction, rather thanparallel to the z-direction. In this case, a shell component describedherein may be located at a perimeter of the sequentially depositedlayers. Additionally, in some instances, the substrate of a methoddescribed herein can be a build pad of a 3D printing system.

An opaque ink or core component, in some embodiments, comprises an inkor core component that transmits no more than about 10% of incidentlight over a 1 centimeter (cm) path length. In some embodiments, anopaque ink or core component transmits no more than about 20% or no morethan about 30% of incident light over a 1 cm path length. In someembodiments, an opaque ink or core component transmits less than about5% of incident light over a 1 cm path length. Incident light, in someembodiments, comprises visible light. In some embodiments, the incidentlight comprises electromagnetic radiation having a wavelength from about350 nm to about 750 nm, from about 400 nm to about 700 nm, from about450 nm to about 600 nm, from about 450 nm to about 500 nm, from about450 nm to about 550 nm, from about 500 nm to about 570 nm, from about500 nm to about 600 nm, from about 600 nm to about 650 nm, from about600 nm to about 700 nm, or from about 650 nm to about 750 nm. Inaddition, in some cases, an opaque ink or core component can beoptically reflective, wherein at least about 10%, at least about 20%, orat least about 30% of incident visible light is reflected by the surfaceof the opaque ink or core component.

In addition, in some embodiments, a method described herein furthercomprises supporting at least one of the layers of the composite inkwith a support material. Any support material not inconsistent with theobjectives of the present disclosure may be used.

A method described herein can also comprise curing the layers of thecomposite ink. In some embodiments, a method of printing a 3D articlefurther comprises subjecting the ink to electromagnetic radiation ofsufficient wavelength and intensity to cure the ink, where curing cancomprise polymerizing one or more polymerizable functional groups of oneor more components of the ink. In some embodiments of printing a 3Darticle, a layer of deposited ink is cured prior to the deposition ofanother or adjacent layer of ink.

In some embodiments, a preselected amount of ink described herein isheated to the appropriate temperature and jetted through the print heador a plurality of print heads of a suitable inkjet printer to form alayer on a print pad in a print chamber. In some embodiments, each layerof ink is deposited according to the preselected CAD parameters. Asuitable print head to deposit the ink, in some embodiments, is apiezoelectric print head. Additional suitable print heads for thedeposition of ink and support material described herein are commerciallyavailable from a variety of ink jet printing apparatus manufacturers.For example, Xerox, Hewlett Packard, or Ricoh print heads may also beused in some instances.

In some embodiments comprising a method of printing a 3D articlecomprising a composite ink as described herein, the composite inkremains substantially fluid upon deposition. In other embodiments, theink exhibits a phase change upon deposition and/or solidifies upondeposition. In some embodiments, the temperature of the printingenvironment can be controlled so that the jetted droplets of inksolidify on contact with the receiving surface. In other embodiments,the jetted droplets of ink do not solidify on contact with the receivingsurface, remaining in a substantially fluid state. In some embodiments,after each layer is deposited, the deposited material is planarized andcured with electromagnetic (e.g., UV) radiation prior to the depositionof the next layer. Optionally, several layers can be deposited beforeplanarization and curing, or multiple layers can be deposited and curedfollowed by one or more layers being deposited and then planarizedwithout curing. Planarization corrects the thickness of one or morelayers prior to curing the material by evening the dispensed material toremove excess material and create a uniformly smooth exposed or flatup-facing surface on the support platform of the printer. In someembodiments, planarization is accomplished with a wiper device, such asa roller, which may be counter-rotating in one or more printingdirections but not counter-rotating in one or more other printingdirections. In some embodiments, the wiper device comprises a roller anda wiper that removes excess material from the roller. In someembodiments, the wiper device is heated. It should be noted that theconsistency of the jetted ink described herein prior to curing, in someembodiments, must be sufficient to retain its shape and not be subjectto excessive viscous drag from the planarizer.

Moreover, a support material, in some embodiments, can be deposited in amanner consistent with that described herein for the ink. The supportmaterial, for example, can be deposited according to the preselected CADparameters such that the support material is adjacent or continuous withone or more layers of the ink. Jetted droplets of the support material,in some embodiments, solidify or freeze on contact with the receivingsurface. In some embodiments, the deposited support material is alsosubjected to planarization.

Layered deposition of the ink and support material can be repeated untilthe 3D article has been formed. In some embodiments, a method ofprinting a 3D article further comprises removing the support materialfrom the ink.

III. 3D Printed Articles

In another aspect, printed 3D articles are described herein. In someembodiments, a printed 3D article is formed from a composite inkdescribed herein. Any composite ink described hereinabove in Section Imay be used. For example, in some cases, the composite ink comprises anoptically transparent or substantially transparent carrier inkcomprising a curable material; and a colorant dispersed in the carrierink in an amount of about 0.01 to 5 weight %, based on the total weightof the composite ink.

In other embodiments, a printed 3D article comprises a core componentcomprising a plurality of layers formed from an opaque ink; and a shellcomponent comprising a plurality of layers formed from a composite inkdescribed herein. Any composite ink described hereinabove in Section Imay be used. For example, in some embodiments, at least one layer of theshell component comprises an optically transparent or substantiallytransparent carrier ink comprising a curable material; and a colorantdispersed in the carrier ink in an amount of about 0.01 to 5 weight %,based on the total weight of the composite ink. Moreover, in someinstances, the layer of the shell component formed from the compositeink has a thickness of about 0.03 to about 5 mm.

Further, in some embodiments, a 3D printed article described hereincomprises a core component and a shell component disposed over the corecomponent in a z-direction. In some cases, the shell component is formedor defined by a plurality of columns of voxels normal or substantiallynormal to a surface of the article. A direction that is “substantially”normal or perpendicular to a surface, plane, or to another direction,for reference purposes herein, is within about 15 degrees, within about10 degrees, or within about 5 degrees of the normal direction. Inaddition, in some instances, at least one column of voxels exhibits asurface color resulting from a combination of colors of a plurality ofvoxels of the column, as described further hereinbelow.

“Color” values for a column of voxels can comprise color values for onevoxel or more than one voxel within the column. Typically, the colorvalues for a column of voxels include color values for all of the voxelsin the column. In addition, the color values can be color valuesaccording to any colorization scheme not inconsistent with theobjectives of the present disclosure, such as a RGB, sRGB, CMY, CMYK,L*a*b*, or Pantone® colorization scheme.

“Transparency” values for a column of voxels can comprise transparencyvalues for one voxel or more than one voxel within the column.Typically, the transparency values for a column of voxels includetransparency values for all of the voxels in the column. In addition,the transparency values can be transparency values according to anytransparency-denoting scheme not inconsistent with the objectives of thepresent disclosure. For example, in some cases, transparency values arevalues between 0 (full transparency) and 1 (full opacity) on an “alpha”scale. Transparency values of voxel data can also correspond to theoptical transparency of the voxel to light having a wavelength betweenabout 350 nm and about 750 nm. For example, a voxel may have an opticaltransparency of less than about 30% transmission, less than about 50%transmission, less than about 70% transmission, greater than about 70%transmission, greater than about 80% transmission, greater than about90% transmission, about 70-80% transmission, about 80-90% transmission,or about 90-100% transmission of incident light between 350 nm and 750nm over the thickness of the voxel or over some other given thickness,such as a thickness between about 0.01 and 10 mm, between about 0.2 and1 mm, between about 0.3 and 0.8 mm, between about 1 and 10 mm, betweenabout 1 and 5 mm, or between about 5 and 10 mm.

The core component of an article described herein can be the innermostregion of the article in the z-direction (which, as described above, isnormal or substantially normal to an exterior surface of the article).Further, the core component of an article can have any color and/orother optical property not inconsistent with the objectives of thepresent disclosure. In some cases, for instance, the core component ofan article described herein is black in color or white in color.Black-colored core components disposed below a shell component can serveto darken one or more colors exhibited or produced by the shellcomponent. Other dark colors in addition to black may also be used.Similarly, a white-colored core component can serve to lighten one ormore colors exhibited or produced by the overlying shell component.Further, light colors other than white may also be used to achieve asimilar effect. Moreover, in some instances, the core component of anarticle described herein is opaque or optically reflective. A corecomponent may also be translucent or transparent. In addition, in someembodiments, the core component of an article described herein islocated or begins at least about 0.5 mm, at least about 1 mm, at leastabout 2 mm, at least about 3 mm, or at least about 4 mm beneath theexterior surface of the article.

As described above, the shell component of an article described hereincan be formed or defined by a plurality of columns of voxels selectedand arranged to provide a desired surface color or other visual surfaceeffect. For instance, in some cases, at least one column of voxelsincludes voxels having different color values and/or differenttransparency values. The use of voxels within a single column havingdifferent color values and/or different transparency values can permitthe column of voxels to exhibit a wide range of color values and/orother visual effects resulting from the combination of the visualcharacteristics of the individual voxels of the column. In this manner,full-color colorization schemes, dithering, and/or halftoning can beachieved by varying color in the z-direction of a 3D printed article. Insome embodiments, a column of voxels includes translucent voxels andopaque voxels, and/or colored voxels and non-colored voxels. A coloredvoxel can be formed from a composite ink described herein, and anon-colored voxel can be formed from an ink or build material that doesnot comprise a colorant or to which one or more colorants have not beenintentionally added.

Further, a shell component of an article described herein can have anydepth or thickness not inconsistent with the objectives of the presentdisclosure. In some cases, a shell component has a depth or thickness ofat least two voxels in the z-direction. In some embodiments, a shellcomponent has a thickness of 2-32 voxels, 2-24 voxels, 2-16 voxels, 4-32voxels, 4-24 voxels, or 4-16 voxels. Other depths or thicknesses arealso possible. In some cases, the total depth or thickness of the shellcomponent is between about 0.03 mm and about 3 mm, between about 0.05 mmand about 2.5 mm, or between about 0.05 mm and about 2 mm. The thicknessor depth of a shell component described herein can be selected based ona desired color level and/or a desired color profile of the article inthe z-direction.

It is to be understood that a “voxel” described herein can be anydesired size, as desired or needed for a given visual effect, providedthe 3D printing system used to form the voxel is capable of providingvoxels of the desired size. The size of a voxel can also correspond to avolume of ink associated with a printing resolution or featureresolution of a 3D printing system used to carry out a method describedherein. The “feature resolution” of an article or system, for referencepurposes herein, can be the smallest controllable physical feature sizeof the article. The feature resolution of an article can be described interms of a unit of distance such as microns (μm), or in terms of dotsper inch (dpi). As understood by one of ordinary skill in the art, ahigher feature resolution corresponds to a higher dpi value but a lowerdistance value in μm. In some cases, an article formed by jetting orextruding an ink described herein can have a feature resolution of about500 μm or less, about 200 μm or less, about 100 μm or less, or about 50μm or less. In some embodiments, an article has a feature resolutionbetween about 50 μm and about 500 μm, between about 50 μm and about 200μm, between about 50 μm and about 100 μm, or between about 100 μm andabout 200 μm. Correspondingly, in some instances, an article describedherein has a feature resolution of at least about 100 dpi, at leastabout 200 dpi, at least about 250 dpi, at least about 400 dpi, or atleast about 500 dpi. In some cases, the feature resolution of an articleis between about 100 dpi and about 600 dpi, between about 100 dpi andabout 250 dpi, or between about 200 dpi and about 600 dpi. In someinstances, a voxel described herein has a volume corresponding to theproduct of the feature resolution (in distance units such as microns)and a layer thickness described herein.

Further, in some cases, an article described herein can comprise a shellcomponent formed from a plurality of differing inks, including aplurality of differing composite inks described herein. The inks candiffer in a layer-by-layer manner or voxel-by-voxel manner. For example,in some embodiments, the shell component of an object described hereincomprises one or more layers or voxels formed from a first composite inkcomprising a first optically transparent or substantially transparentcarrier ink comprising a curable material, and a first colorantdispersed in the first carrier ink in an amount of about 0.01 to 5weight %, based on the total weight of the first composite ink; and oneor more layers or voxels formed from a second composite ink comprising asecond optically transparent or substantially transparent carrier inkcomprising a curable material, and a second colorant dispersed in thesecond carrier ink in an amount of about 0.01 to 5 weight %, based onthe total weight of the second composite ink. In such cases, the firstcomposite ink and the second composite ink can be different inks. Forexample, in some embodiments, the chemical identity and/or amount of thefirst colorant of the first composite ink can differ from the chemicalidentity and/or amount of the second colorant of the second compositeink. In a similar manner, the shell component of an article describedherein can comprise one or more layers or voxels formed from n compositeinks that are the same or different from one another, where n can be upto 5, up to 10, up to 20, or more than 20.

Some embodiments described herein are further illustrated in thefollowing non-limiting examples.

Example 1 Composite Inks

Composite inks according to some embodiments described herein wereprepared as follows. Various commercial pigments were disposed incarrier inks described herein having an optical transparency of over 90%transmission. Specifically, the carrier inks included urethane(meth)acrylate oligomers (15-25 wt. %), non-oligomericmono(meth)acrylates (28-42 wt. %), non-oligomeric di(meth)acrylates(28-36 wt. %), non-oligomeric tri(meth)acrylates (8-12 wt. %),stabilizer (0.1-0.2 wt. %), and photoinitiator (2-4 wt. %). Thecommercial pigments included Sun UVDJ354, Sun UVDj322, Sun UVDJ1 50, SunUVDj350, RJA D3010-FX-Y150, RJA D3410-FX-Y150, and others provided inTable I below. The composite inks were then jetted into layers havingvarious thicknesses and their chromatic properties measured. The chromavalues of some composite inks as a function of layer thickness areplotted in FIG. 1. For a given colorant, the optimum absorption of lightoccurs at a certain amount of colorant. Above this optimum, the colorcan become too dark (when plotted lines begin curving downward). Belowthis optimum, the color can be too light.

Cyan, yellow, and magenta pigment loads were designed to impart themaximum chromaticity at 0.3 mm and 0.15 mm layer thickness. Forblack-colored ink, the pigment load was chosen to impart the maximumoptical density (OD) or the lowest lightness (L*). FIG. 2 illustratesplots of optical density versus layer thickness for variousblack-colored inks. FIG. 3 illustrates plots of lightness versus layerthickness for the same black-colored inks.

Additional results are provided in Table I below.

TABLE I Pigment Loading Amounts wt % for 0.30 wt % for 0.15 mm coloredmm colored Pigment layer layer UVDJ354 (cyan, Sun Chemical) 0.053 0.11UVDJ150 (yellow, Sun Chemical) 0.069 0.14 UVDJ322 (magenta, SunChemical) 0.059 0.12 UVDJ350 (yellow, Sun Chemical) 0.060 0.12D3010-FX-Y150 (yellow, RJA 0.041 0.082 Dispersions) D3410-FX-Y150(yellow, RJA 0.051 0.10 Dispersions) UVDJ107 (black, Sun Chemical) 0.150.30 D3410-FX-K (black, RJA 0.15 0.30 Dispersions) D3010-FX-K (black,RJA 0.15 0.30 Dispersions) 9B989 (black, Penn Colors) 0.15 0.30 9B898(black, Penn Colors) 0.15 0.30

Example 2 Printed 3D Article

A printed 3D article according to one embodiment described herein wasprinted as illustrated in FIG. 4. With reference to FIG. 4, the article(400) comprises a core component (410) formed from a plurality of opaquewhite voxels (411) and a shell component (420) disposed over the corecomponent (410) in a z-direction (z). The shell component (420) isdefined by a plurality of columns (430) of voxels (431) substantiallynormal to a surface (440) of the article (400). The voxels (431) of theshell component (420) are formed from a composite ink described herein.In addition, at least some of the columns (430) of voxels (431) exhibita surface color (450) resulting from a combination of the colors of aplurality of the underlying voxels (431). For example, the green surfacecolor of the seventh column in FIG. 4 exhibits a green surface color(450) resulting from the combination of the underlying cyan and yellowvoxels (431). Similarly, the dark pink surface color (450) of the sixthcolumn results from the combination of the underlying magenta and blackvoxels (431).

As illustrated in FIG. 4, the core component (410) and the shellcomponent (420) are disposed on a substrate (460). This substrate (460)can be the build pad of a 3D printing system or a previously depositedlayer of build material or support material.

Further, it is to be understood that the surface (440) in FIG. 4 is onlyone exterior surface of the article (400), or one portion of oneexterior surface of the article (400). Additionally, FIG. 4 presents asectional view of the article (400).

All patent documents referred to herein are incorporated by reference intheir entireties. Various embodiments of the invention have beendescribed in fulfillment of the various objectives of the invention. Itshould be recognized that these embodiments are merely illustrative ofthe principles of the present invention. Numerous modifications andadaptations thereof will be readily apparent to those skilled in the artwithout departing from the spirit and scope of the invention.

That which is claimed:
 1. A composite ink for use in a three-dimensionalprinting system comprising: a carrier ink comprising a curable material;and a colorant dispersed in the carrier ink in an amount of 0.01 to 5weight %, based on the total weight of the composite ink, wherein achroma of the composite ink at a given thickness of the composite ink iswithin 20% of a maximum chroma of the colorant in the composite ink, andwherein the carrier ink has an optical transparency of at least 80%transmission between 350 nm and 750 nm at a thickness of 0.01 to 10 mm.2. The composite ink of claim 1, wherein the colorant comprises aparticulate pigment.
 3. The composite ink of claim 2, wherein theparticulate pigment has an average particle size of 50-1000 nm.
 4. Thecomposite ink of claim 3, wherein the average particle size is 70-200nm.
 5. The composite ink of claim 1, wherein the colorant comprises amolecular dye.
 6. The composite ink of claim 1, wherein the curablematerial comprises one or more species of (meth)acrylates.
 7. Thecomposite ink of claim 1, wherein the curable material comprises one ormore oligomeric materials.
 8. The composite ink of claim 7, wherein theone or more oligomeric materials comprise a urethane (meth)acrylate. 9.The composite ink of claim 1, wherein the carrier ink comprises 10-95weight % curable material, based on the total weight of the carrier ink.10. The composite ink of claim 1 further comprising one or moreadditives selected from the group consisting of photoinitiators,inhibitors, stabilizing agents, sensitizers, and combinations thereof.11. The composite ink of claim 1, wherein the composite ink has aviscosity ranging from 8.0 cP to 19.0 cP at a temperature of 65° C.measured according to ASTM standard D2983.
 12. The composite ink ofclaim 1, wherein the composite ink has a viscosity ranging from 8.0 cPto 14.0 cP at a temperature of 80° C. when measured according to ASTMstandard D2983.